Both automated and hand operated spray applicators are used extensively in industry to apply coatings of various types to objects during manufacture and assembly. Automobile vehicle bodies commonly are coated using robotic devices with spray applicators. The evolution of applicators has followed both the need and desire to improve spraying efficiency and minimize waste of the coating material that is applied.
It is known to use atomizing applicators to reduce the amount of overspray and ensure that the object is uniformly covered. In one known type of atomizing applicator, a bell cup having a narrow base and a wider forward edge is rotated at high speed. The coating material, such as paint, is provided to the inside of the rotating cup. The paint or other coating moves outwardly along the substantially smooth inner surface of the bell cup and is discharged from the forward edge of the bell cup as a result of centrifugal force from the rotating cup. The coating is atomized into a fine mist as it leaves the bell cup surface. The velocity of the mist is determined by many factors, including the shape of the bell cup, but generally is at an angle both forwardly and outwardly from the bell cup. To move the coating more forwardly and less outwardly from the discharge path off the surface of the bell cup, it is known to use shaping air streams to confine and direct the atomized coating toward the target object. It is also known to charge the atomized mist with electrical potential and to ground the object being coated so that the coating material is attracted to the object, further reducing overspray and improving coverage on irregularly shaped target objects.
While rotary atomizing applicators as described above have been used successfully in many industries, it is desirable to further reduce the waste of sprayed material. The natural direction of the atomized particles discharged from the forward edge of the rotary bell cup has a significant radially outward component. Shaping air streams have been used to attempt to confine the outward divergence of the spray pattern by flowing an air stream along the spray pattern outwardly from the bell cup. Known shaping air systems have used high pressure air at the forward edge of the bell cup, high air volumes and/or air directed at the lower base of the bell cup to follow along the bell cup. However, these systems have not been completely effective in controlling the outward velocity of the coating material. High velocity coating particles, such as metal flakes in paint, can pass through the high pressure air streams at the bell cup edge used in some shaping air systems. Shaping air systems using large air volumes are limited in pattern size. Shaping air systems in which air follows the outer surface of the bell cup release the shaping air streams at outward trajectories following essentially the same angle as the exterior of the cup, and not directly at the target object. Accordingly, in some situations it has been difficult to confine all of the spray to a narrow pattern when small target objects are being coated. Coating inconsistencies have occurred when particles in the coating, such as metal flake in paint are confined by the shaping air less consistently than the coating mist in which the particles are contained. The result is a separation of the metal flakes from the paint, and inconsistent coverage of metal flakes on the coated object.
What are needed in the art are a spray applicator head configuration and a method for controlling spray patterns which smoothly and evenly confine the spray to a narrow pattern ahead of the applicator.